Thyroid Flashcards
A 79-year-old woman is admitted to hospital following a fall. During the initial clerking she complained of feeling cold all the time. Thyroid function tests (TFTs) were therefore ordered:
- Free T47.1 pmol/l
- TSH14.3 mu/l
What is the most appropriate action?
- Repeat TFTs in 3 months
- Start levothyroxine 25mcg od
- Start levothyroxine 50mcg od
- Start levothyroxine 100mcg od
- Start carbimazole 10mg od
Start levothyroxine 25mcg od
This lady has hypothyroidism as evidenced by the low free T4 and raised TSH. Given her age levothyroxine should be introduced slowly starting with a dose of 25mcg od.
Hypothyroidism: management
Key points
- initial starting dose of levothyroxine should be lower in elderly patients and those with ischaemic heart disease. The BNF recommends that for patients with cardiac disease, severe hypothyroidism or patients over 50 years the initial starting dose should be 25mcg od with dose slowly titrated. Other patients should be started on a dose of 50-100mcg od
- following a change in thyroxine dose thyroid function tests should be checked after 8-12 weeks
- the therapeutic goal is ‘normalisation’ of the thyroid stimulating hormone (TSH) level. As the majority of unaffected people have a TSH value 0.5-2.5 mU/l it is now thought preferable to aim for a TSH in this range
- women with established hypothyroidism who become pregnant should have their dose increased ‘by at least 25-50 micrograms levothyroxine’* due to the increased demands of pregnancy. The TSH should be monitored carefully, aiming for a low-normal value
- there is no evidence to support combination therapy with levothyroxine and liothyronine
Side-effects of thyroxine therapy
- hyperthyroidism: due to over treatment
- reduced bone mineral density
- worsening of angina
- atrial fibrillation
Interactions
- iron, calcium carbonate
absorption of levothyroxine reduced, give at least 4 hours apart
A 30-year-old woman presents with a severe sore throat. Her symptoms started around ten days ago and have got progressively worse. Six weeks ago she was diagnosed with Grave’s disease and started on carbimazole 30mg od.
Select the two most relevant tests to order in this situation.
- A.Carbimazole level
- B.Full blood count
- C.Thyroid function tests
- D.Urea and electrolytes
- E.Throat swab
Correct answer: B C
- Neutropaenia and agranulocytosis are the most important adverse effects to be aware of in patients taking carbimazole. As a result patients should be specifically warned about sore throats when treatment is initiated. A full blood count is needed to exclude this as a possibility.
- Thyroid function tests should also be performed to see whether the patient is still thyrotoxic and to ensure they have not become hypothyroid.
Carbimazole levels are not used in clinical practice.
Carbimazole
- Carbimazole is used in the management of thyrotoxicosis. It is typically given in high doses for 6 weeks until the patient becomes euthyroid before being reduced.
Mechanism of action
- blocks thyroid peroxidase from coupling and iodinating the tyrosine residues on thyroglobulin → reducing thyroid hormone production
- in contrast propylthiouracil as well as this central mechanism of action also has a peripheral action by inhibiting 5’-deiodinase which reduces peripheral conversion of T4 to T3
Adverse effects
- agranulocytosis
- crosses the placenta, but may be used in low doses during pregnancy
A 63-year-old woman presents to her GP for review. Her past medical history includes hypothyroidism for which she currently takes levothyroxine 100mcg. She is currently well and has no symptoms of note. Her last thyroid function tests (TFTs) 12 months ago on this dose were normal.
- Free T418.5 pmol/l
- TSH0.1 mu/l
What is the most appropriate action?
- Make no changes to the current dose
- Increase dose to levothyroxine 150mcg od
- Decrease dose to levothyroxine 75mcg od
- Decrease dose to levothyroxine 50mcg od
- Add carbimazole 10mg od
Decrease dose to levothyroxine 75mcg od
The most recent TFTs show a suppressed TSH indicating over replacement. Even though she is asymptomatic the dose should be decreased to reduce the risk of osteoporosis and atrial fibrillation. The BNF recommends adjusting the dose by 25mcg in this age group.
